Apparatus for measuring the pre-tension of a threaded bolt

Abstract

Apparatus for measuring the pre-tension of a threaded bolt which is elongated by means of a tensioning unit and a screwed-in tensioning bolt; a measuring rod is inserted into a central hole in the threaded bolt and the difference in length is determined by means of a length measuring device. The measuring rod is guided in the housing of the tensioning unit, secured against rotation, and is threaded to engage a threaded bushing. The threaded bushing is longitudinally movable and secured against rotation in a bushing having external teeth. Rotation of the tensioning bolt is transmitted via gears to the threads on the measuring rod and converted into an up or down movement. The measurement may be made when the measuring rod comes to rest at the lowest point of the central hole.

What is claimed is: 
     
       1. In an apparatus for measuring the pre-tension of a threaded bolt useful for closing a reactor pressure vessel comprising a demountable automatic tensioning unit having a tensioning bolt for screwing into a threaded bolt and elongating it, there being a central hole in the tensioning bolt and in the threaded bolt for receiving a measuring rod and a measuring device for determining the difference in length between the threaded bolt plus the tensioning bolt and the measuring rod, the improvement comprising: a tensioning unit housing adapted to engage the tensioning bolt and including a yoke provided with an opening having a fitted key,   a measuring rod passing through the yoke opening and having at its upper end a longitudinal slot for receiving the fitted key and securing the rod against rotation, and further having in the vicinity of the tensioning unit a threaded portion for engaging a threaded bushing,   a threaded bushing for engaging the threaded rod,   a hollow bushing for containing the threading bushing and securing it against rotation while permitting limited longitudinal motion relative to the rod,   internal gearing connected to the tensioning bolt,   intermediate gears mounted on spindles carried, secure against rotation, by the measuring rod for meshing with the external teeth of the hollow bushing and the internal gearing connected to the tensioning bolt,   and a length measuring device carried by the measuring rod and resting on a surface connected to the tensioning bolt or the threaded bolt.   
     
     
       2. In an apparatus in accordance with claim 1, the further improvement that the intermediate gears such consist of two gears of differing diameters mounted on a shaft with a gear of one diameter meshing with the external teeth of the bushing and a gear of the other diameter meshing with the internal gearing connected to the tensioning bolt. 
     
     
       3. In an apparatus in accordance with claim 2, the improvement in which the bushing having external gear teeth is provided with elongated holes in which the threaded bushing is longitudinally movable. 
     
     
       4. In an apparatus in accordance with claim 1 or claim 3, the improvement in which the bushing having external gear teeth is carried on an end face of a tube connected to the tensioning bolt and surrounding the measuring rod 
     
     
       5. In apparatus in accordance with claim 1 or claim 2, the improvement in which the spindles carrying the intermediate gears are supported by a plate having a hole for passage of the measuring rod and having a key for engaging the longitudinal slot in the measuring rod and securing the plate against rotation. 
     
     
       6. In an apparatus in accordance with claim 5, the improvement in which the plate is supported on an upper end face of the bushing having external gear teeth. 
     
     
       7. In an apparatus in accordance with claim 5, the improvement in which the intermediate gears are carried on upright spindless. 
     
     
       8. In an apparatus according to claim 1, the improvement in which the thread on the measuring rod and the thread of the threaded bushing are trapezoidal in profile.